Probing the Mechanism of Surface-Enhanced Raman Scattering in 2D Nb₂CTₓ MXene*

MXenes have attracted considerable interest in surface-enhanced Raman scattering (SERS) owing to their unique electronic properties and excellent hydrophilicity. Among them, niobium carbide (Nb₂C Tₓ) remains relatively underexplored for SERS applications. In this work, we systematically investigated the SERS mechanism of Nb₂CTₓ MXene using methylene blue (MB) and crystal violet (CV) as probe molecules under 532 nm and 488 nm laser excitation. Our results show that Raman enhancement depends strongly on the interplay between excitation wavelength and probe molecules. Notably, MB exhibited an enhancement factor (EF) of 2.12 × 10⁶ under 532 nm excitation, nearly two orders of magnitude higher than that of CV (2.65 × 10⁴). This significant difference is attributed to a resonance charge-transfer transition induced by light within the MB–Nb₂CTₓ system. The contrasting EF values for MB and CV highlight the potential of chemical-mechanism-dominated SERS in enabling selective molecular detection. These findings provide mechanistic insights into SERS enhancement and establish Nb₂CTₓ MXene as a cost-effective 2D platform for selective SERS-based sensing applications.